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Revision 1.7 by root, Fri Mar 23 15:10:55 2007 UTC vs.
Revision 1.112 by root, Mon Sep 29 03:09:27 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	3	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		4
		5	=encoding utf-8
		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
8		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
11	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
12	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
13	I<fast>. To reach the latter goal it was written in C.	38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overridden) with no overhead due to emulation (by inheriting constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
14		47
15	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
16	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
17	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
18	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
19	reports for other reasons.	52	reports for other reasons.
20		53
21	See COMPARISON, below, for a comparison to some other JSON modules.	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		55	vice versa.
22		56
23	=head2 FEATURES	57	=head2 FEATURES
24		58
25	=over 4	59	=over 4
26		60
27	=item * correct handling of unicode issues	61	=item * correct Unicode handling
28		62
29	This module knows how to handle Unicode, and even documents how it does so.	63	This module knows how to handle Unicode, documents how and when it does
		64	so, and even documents what "correct" means.
30		65
31	=item * round-trip integrity	66	=item * round-trip integrity
32		67
33	When you serialise a perl data structure using only datatypes supported	68	When you serialise a perl data structure using only data types supported
34	by JSON, the deserialised data structure is identical on the Perl level.	69	by JSON, the deserialised data structure is identical on the Perl level.
35	(e.g. the string "2.0" doesn't suddenly become "2").	70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		71	like a number). There minor I<are> exceptions to this, read the MAPPING
		72	section below to learn about those.
36		73
37	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
38		75
39	There is no guessing, no generating of illegal JSON strings by default,	76	There is no guessing, no generating of illegal JSON texts by default,
40	and only JSON is accepted as input (the latter is a security feature).	77	and only JSON is accepted as input by default (the latter is a security
		78	feature).
41		79
42	=item * fast	80	=item * fast
43		81
44	compared to other JSON modules, this module compares favourably.	82	Compared to other JSON modules and other serialisers such as Storable,
		83	this module usually compares favourably in terms of speed, too.
45		84
46	=item * simple to use	85	=item * simple to use
47		86
48	This module has both a simple functional interface as well as an OO	87	This module has both a simple functional interface as well as an object
49	interface.	88	oriented interface interface.
50		89
51	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
52		91
53	You can choose between the most compact format possible, a pure-ascii	92	You can choose between the most compact guaranteed-single-line format
54	format, or a pretty-printed format. Or you can combine those features in	93	possible (nice for simple line-based protocols), a pure-ASCII format
55	whatever way you like.	94	(for when your transport is not 8-bit clean, still supports the whole
		95	Unicode range), or a pretty-printed format (for when you want to read that
		96	stuff). Or you can combine those features in whatever way you like.
56		97
57	=back	98	=back
58		99
59	=cut	100	=cut
60		101
61	package JSON::XS;	102	package JSON::XS;
62		103
63	BEGIN {	104	no warnings;
		105	use strict;
		106
64	$VERSION = '0.2';	107	our $VERSION = '2.23';
65	@ISA = qw(Exporter);	108	our @ISA = qw(Exporter);
66		109
67	@EXPORT = qw(to_json from_json);	110	our @EXPORT = qw(encode_json decode_json to_json from_json);
68	require Exporter;
69		111
		112	sub to_json($) {
70	require XSLoader;	113	require Carp;
71	XSLoader::load JSON::XS::, $VERSION;	114	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
72	}	115	}
73		116
		117	sub from_json($) {
		118	require Carp;
		119	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		120	}
		121
		122	use Exporter;
		123	use XSLoader;
		124
74	=head1 FUNCTIONAL INTERFACE	125	=head1 FUNCTIONAL INTERFACE
75		126
76	The following convinience methods are provided by this module. They are	127	The following convenience methods are provided by this module. They are
77	exported by default:	128	exported by default:
78		129
79	=over 4	130	=over 4
80		131
81	=item $json_string = to_json $perl_scalar	132	=item $json_text = encode_json $perl_scalar
82		133
83	Converts the given Perl data structure (a simple scalar or a reference to	134	Converts the given Perl data structure to a UTF-8 encoded, binary string
84	a hash or array) to a UTF-8 encoded, binary string (that is, the string contains	135	(that is, the string contains octets only). Croaks on error.
85	octets only). Croaks on error.
86		136
87	This function call is functionally identical to C<< JSON::XS->new->utf8	137	This function call is functionally identical to:
88	(1)->encode ($perl_scalar) >>.
89		138
		139	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		140
		141	Except being faster.
		142
90	=item $perl_scalar = from_json $json_string	143	=item $perl_scalar = decode_json $json_text
91		144
92	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to	145	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
93	parse that as an UTF-8 encoded JSON string, returning the resulting simple	146	to parse that as an UTF-8 encoded JSON text, returning the resulting
94	scalar or reference. Croaks on error.	147	reference. Croaks on error.
95		148
96	This function call is functionally identical to C<< JSON::XS->new->utf8	149	This function call is functionally identical to:
97	(1)->decode ($json_string) >>.	150
		151	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		152
		153	Except being faster.
		154
		155	=item $is_boolean = JSON::XS::is_bool $scalar
		156
		157	Returns true if the passed scalar represents either JSON::XS::true or
		158	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		159	and are used to represent JSON C<true> and C<false> values in Perl.
		160
		161	See MAPPING, below, for more information on how JSON values are mapped to
		162	Perl.
98		163
99	=back	164	=back
		165
		166
		167	=head1 A FEW NOTES ON UNICODE AND PERL
		168
		169	Since this often leads to confusion, here are a few very clear words on
		170	how Unicode works in Perl, modulo bugs.
		171
		172	=over 4
		173
		174	=item 1. Perl strings can store characters with ordinal values > 255.
		175
		176	This enables you to store Unicode characters as single characters in a
		177	Perl string - very natural.
		178
		179	=item 2. Perl does I<not> associate an encoding with your strings.
		180
		181	... until you force it to, e.g. when matching it against a regex, or
		182	printing the scalar to a file, in which case Perl either interprets your
		183	string as locale-encoded text, octets/binary, or as Unicode, depending
		184	on various settings. In no case is an encoding stored together with your
		185	data, it is I<use> that decides encoding, not any magical meta data.
		186
		187	=item 3. The internal utf-8 flag has no meaning with regards to the
		188	encoding of your string.
		189
		190	Just ignore that flag unless you debug a Perl bug, a module written in
		191	XS or want to dive into the internals of perl. Otherwise it will only
		192	confuse you, as, despite the name, it says nothing about how your string
		193	is encoded. You can have Unicode strings with that flag set, with that
		194	flag clear, and you can have binary data with that flag set and that flag
		195	clear. Other possibilities exist, too.
		196
		197	If you didn't know about that flag, just the better, pretend it doesn't
		198	exist.
		199
		200	=item 4. A "Unicode String" is simply a string where each character can be
		201	validly interpreted as a Unicode code point.
		202
		203	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		204	Unicode string encoded in UTF-8, giving you a binary string.
		205
		206	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		207
		208	It's a fact. Learn to live with it.
		209
		210	=back
		211
		212	I hope this helps :)
		213
100		214
101	=head1 OBJECT-ORIENTED INTERFACE	215	=head1 OBJECT-ORIENTED INTERFACE
102		216
103	The object oriented interface lets you configure your own encoding or	217	The object oriented interface lets you configure your own encoding or
104	decoding style, within the limits of supported formats.	218	decoding style, within the limits of supported formats.
…		…
111	strings. All boolean flags described below are by default I<disabled>.	225	strings. All boolean flags described below are by default I<disabled>.
112		226
113	The mutators for flags all return the JSON object again and thus calls can	227	The mutators for flags all return the JSON object again and thus calls can
114	be chained:	228	be chained:
115		229
116	my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})	230	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
117	=> {"a": [1, 2]}	231	=> {"a": [1, 2]}
118		232
119	=item $json = $json->ascii ([$enable])	233	=item $json = $json->ascii ([$enable])
120		234
		235	=item $enabled = $json->get_ascii
		236
121	If C<$enable> is true (or missing), then the C<encode> method will	237	If C<$enable> is true (or missing), then the C<encode> method will not
122	not generate characters outside the code range C<0..127>. Any unicode	238	generate characters outside the code range C<0..127> (which is ASCII). Any
123	characters outside that range will be escaped using either a single	239	Unicode characters outside that range will be escaped using either a
124	\uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per	240	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
125	RFC4627.	241	as per RFC4627. The resulting encoded JSON text can be treated as a native
		242	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		243	or any other superset of ASCII.
126		244
127	If C<$enable> is false, then the C<encode> method will not escape Unicode	245	If C<$enable> is false, then the C<encode> method will not escape Unicode
128	characters unless necessary.	246	characters unless required by the JSON syntax or other flags. This results
		247	in a faster and more compact format.
129		248
		249	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		250	document.
		251
		252	The main use for this flag is to produce JSON texts that can be
		253	transmitted over a 7-bit channel, as the encoded JSON texts will not
		254	contain any 8 bit characters.
		255
130	JSON::XS->new->ascii (1)->encode (chr 0x10401)	256	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
131	=> \ud801\udc01	257	=> ["\ud801\udc01"]
		258
		259	=item $json = $json->latin1 ([$enable])
		260
		261	=item $enabled = $json->get_latin1
		262
		263	If C<$enable> is true (or missing), then the C<encode> method will encode
		264	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		265	outside the code range C<0..255>. The resulting string can be treated as a
		266	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		267	will not be affected in any way by this flag, as C<decode> by default
		268	expects Unicode, which is a strict superset of latin1.
		269
		270	If C<$enable> is false, then the C<encode> method will not escape Unicode
		271	characters unless required by the JSON syntax or other flags.
		272
		273	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		274	document.
		275
		276	The main use for this flag is efficiently encoding binary data as JSON
		277	text, as most octets will not be escaped, resulting in a smaller encoded
		278	size. The disadvantage is that the resulting JSON text is encoded
		279	in latin1 (and must correctly be treated as such when storing and
		280	transferring), a rare encoding for JSON. It is therefore most useful when
		281	you want to store data structures known to contain binary data efficiently
		282	in files or databases, not when talking to other JSON encoders/decoders.
		283
		284	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		285	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
132		286
133	=item $json = $json->utf8 ([$enable])	287	=item $json = $json->utf8 ([$enable])
134		288
		289	=item $enabled = $json->get_utf8
		290
135	If C<$enable> is true (or missing), then the C<encode> method will encode	291	If C<$enable> is true (or missing), then the C<encode> method will encode
136	the JSON string into UTF-8, as required by many protocols, while the	292	the JSON result into UTF-8, as required by many protocols, while the
137	C<decode> method expects to be handled an UTF-8-encoded string. Please	293	C<decode> method expects to be handled an UTF-8-encoded string. Please
138	note that UTF-8-encoded strings do not contain any characters outside the	294	note that UTF-8-encoded strings do not contain any characters outside the
139	range C<0..255>, they are thus useful for bytewise/binary I/O.	295	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		296	versions, enabling this option might enable autodetection of the UTF-16
		297	and UTF-32 encoding families, as described in RFC4627.
140		298
141	If C<$enable> is false, then the C<encode> method will return the JSON	299	If C<$enable> is false, then the C<encode> method will return the JSON
142	string as a (non-encoded) unicode string, while C<decode> expects thus a	300	string as a (non-encoded) Unicode string, while C<decode> expects thus a
143	unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	301	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
144	to be done yourself, e.g. using the Encode module.	302	to be done yourself, e.g. using the Encode module.
		303
		304	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		305	document.
		306
		307	Example, output UTF-16BE-encoded JSON:
		308
		309	use Encode;
		310	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		311
		312	Example, decode UTF-32LE-encoded JSON:
		313
		314	use Encode;
		315	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
145		316
146	=item $json = $json->pretty ([$enable])	317	=item $json = $json->pretty ([$enable])
147		318
148	This enables (or disables) all of the C<indent>, C<space_before> and	319	This enables (or disables) all of the C<indent>, C<space_before> and
149	C<space_after> (and in the future possibly more) flags in one call to	320	C<space_after> (and in the future possibly more) flags in one call to
150	generate the most readable (or most compact) form possible.	321	generate the most readable (or most compact) form possible.
		322
		323	Example, pretty-print some simple structure:
151		324
152	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})	325	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
153	=>	326	=>
154	{	327	{
155	"a" : [	328	"a" : [
…		…
158	]	331	]
159	}	332	}
160		333
161	=item $json = $json->indent ([$enable])	334	=item $json = $json->indent ([$enable])
162		335
		336	=item $enabled = $json->get_indent
		337
163	If C<$enable> is true (or missing), then the C<encode> method will use a multiline	338	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
164	format as output, putting every array member or object/hash key-value pair	339	format as output, putting every array member or object/hash key-value pair
165	into its own line, identing them properly.	340	into its own line, indenting them properly.
166		341
167	If C<$enable> is false, no newlines or indenting will be produced, and the	342	If C<$enable> is false, no newlines or indenting will be produced, and the
168	resulting JSON strings is guarenteed not to contain any C<newlines>.	343	resulting JSON text is guaranteed not to contain any C<newlines>.
169		344
170	This setting has no effect when decoding JSON strings.	345	This setting has no effect when decoding JSON texts.
171		346
172	=item $json = $json->space_before ([$enable])	347	=item $json = $json->space_before ([$enable])
		348
		349	=item $enabled = $json->get_space_before
173		350
174	If C<$enable> is true (or missing), then the C<encode> method will add an extra	351	If C<$enable> is true (or missing), then the C<encode> method will add an extra
175	optional space before the C<:> separating keys from values in JSON objects.	352	optional space before the C<:> separating keys from values in JSON objects.
176		353
177	If C<$enable> is false, then the C<encode> method will not add any extra	354	If C<$enable> is false, then the C<encode> method will not add any extra
178	space at those places.	355	space at those places.
179		356
180	This setting has no effect when decoding JSON strings. You will also most	357	This setting has no effect when decoding JSON texts. You will also
181	likely combine this setting with C<space_after>.	358	most likely combine this setting with C<space_after>.
		359
		360	Example, space_before enabled, space_after and indent disabled:
		361
		362	{"key" :"value"}
182		363
183	=item $json = $json->space_after ([$enable])	364	=item $json = $json->space_after ([$enable])
		365
		366	=item $enabled = $json->get_space_after
184		367
185	If C<$enable> is true (or missing), then the C<encode> method will add an extra	368	If C<$enable> is true (or missing), then the C<encode> method will add an extra
186	optional space after the C<:> separating keys from values in JSON objects	369	optional space after the C<:> separating keys from values in JSON objects
187	and extra whitespace after the C<,> separating key-value pairs and array	370	and extra whitespace after the C<,> separating key-value pairs and array
188	members.	371	members.
189		372
190	If C<$enable> is false, then the C<encode> method will not add any extra	373	If C<$enable> is false, then the C<encode> method will not add any extra
191	space at those places.	374	space at those places.
192		375
193	This setting has no effect when decoding JSON strings.	376	This setting has no effect when decoding JSON texts.
		377
		378	Example, space_before and indent disabled, space_after enabled:
		379
		380	{"key": "value"}
		381
		382	=item $json = $json->relaxed ([$enable])
		383
		384	=item $enabled = $json->get_relaxed
		385
		386	If C<$enable> is true (or missing), then C<decode> will accept some
		387	extensions to normal JSON syntax (see below). C<encode> will not be
		388	affected in anyway. I<Be aware that this option makes you accept invalid
		389	JSON texts as if they were valid!>. I suggest only to use this option to
		390	parse application-specific files written by humans (configuration files,
		391	resource files etc.)
		392
		393	If C<$enable> is false (the default), then C<decode> will only accept
		394	valid JSON texts.
		395
		396	Currently accepted extensions are:
		397
		398	=over 4
		399
		400	=item * list items can have an end-comma
		401
		402	JSON I<separates> array elements and key-value pairs with commas. This
		403	can be annoying if you write JSON texts manually and want to be able to
		404	quickly append elements, so this extension accepts comma at the end of
		405	such items not just between them:
		406
		407	[
		408	1,
		409	2, <- this comma not normally allowed
		410	]
		411	{
		412	"k1": "v1",
		413	"k2": "v2", <- this comma not normally allowed
		414	}
		415
		416	=item * shell-style '#'-comments
		417
		418	Whenever JSON allows whitespace, shell-style comments are additionally
		419	allowed. They are terminated by the first carriage-return or line-feed
		420	character, after which more white-space and comments are allowed.
		421
		422	[
		423	1, # this comment not allowed in JSON
		424	# neither this one...
		425	]
		426
		427	=back
194		428
195	=item $json = $json->canonical ([$enable])	429	=item $json = $json->canonical ([$enable])
		430
		431	=item $enabled = $json->get_canonical
196		432
197	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	433	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
198	by sorting their keys. This is adding a comparatively high overhead.	434	by sorting their keys. This is adding a comparatively high overhead.
199		435
200	If C<$enable> is false, then the C<encode> method will output key-value	436	If C<$enable> is false, then the C<encode> method will output key-value
201	pairs in the order Perl stores them (which will likely change between runs	437	pairs in the order Perl stores them (which will likely change between runs
202	of the same script).	438	of the same script).
203		439
204	This option is useful if you want the same data structure to be encoded as	440	This option is useful if you want the same data structure to be encoded as
205	the same JSON string (given the same overall settings). If it is disabled,	441	the same JSON text (given the same overall settings). If it is disabled,
206	the same hash migh be encoded differently even if contains the same data,	442	the same hash might be encoded differently even if contains the same data,
207	as key-value pairs have no inherent ordering in Perl.	443	as key-value pairs have no inherent ordering in Perl.
208		444
209	This setting has no effect when decoding JSON strings.	445	This setting has no effect when decoding JSON texts.
210		446
211	=item $json = $json->allow_nonref ([$enable])	447	=item $json = $json->allow_nonref ([$enable])
		448
		449	=item $enabled = $json->get_allow_nonref
212		450
213	If C<$enable> is true (or missing), then the C<encode> method can convert a	451	If C<$enable> is true (or missing), then the C<encode> method can convert a
214	non-reference into its corresponding string, number or null JSON value,	452	non-reference into its corresponding string, number or null JSON value,
215	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON	453	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
216	values instead of croaking.	454	values instead of croaking.
217		455
218	If C<$enable> is false, then the C<encode> method will croak if it isn't	456	If C<$enable> is false, then the C<encode> method will croak if it isn't
219	passed an arrayref or hashref, as JSON strings must either be an object	457	passed an arrayref or hashref, as JSON texts must either be an object
220	or array. Likewise, C<decode> will croak if given something that is not a	458	or array. Likewise, C<decode> will croak if given something that is not a
221	JSON object or array.	459	JSON object or array.
222		460
		461	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		462	resulting in an invalid JSON text:
		463
		464	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		465	=> "Hello, World!"
		466
		467	=item $json = $json->allow_unknown ([$enable])
		468
		469	=item $enabled = $json->get_allow_unknown
		470
		471	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		472	exception when it encounters values it cannot represent in JSON (for
		473	example, filehandles) but instead will encode a JSON C<null> value. Note
		474	that blessed objects are not included here and are handled separately by
		475	c<allow_nonref>.
		476
		477	If C<$enable> is false (the default), then C<encode> will throw an
		478	exception when it encounters anything it cannot encode as JSON.
		479
		480	This option does not affect C<decode> in any way, and it is recommended to
		481	leave it off unless you know your communications partner.
		482
		483	=item $json = $json->allow_blessed ([$enable])
		484
		485	=item $enabled = $json->get_allow_blessed
		486
		487	If C<$enable> is true (or missing), then the C<encode> method will not
		488	barf when it encounters a blessed reference. Instead, the value of the
		489	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		490	disabled or no C<TO_JSON> method found) or a representation of the
		491	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		492	encoded. Has no effect on C<decode>.
		493
		494	If C<$enable> is false (the default), then C<encode> will throw an
		495	exception when it encounters a blessed object.
		496
		497	=item $json = $json->convert_blessed ([$enable])
		498
		499	=item $enabled = $json->get_convert_blessed
		500
		501	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		502	blessed object, will check for the availability of the C<TO_JSON> method
		503	on the object's class. If found, it will be called in scalar context
		504	and the resulting scalar will be encoded instead of the object. If no
		505	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		506	to do.
		507
		508	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		509	returns other blessed objects, those will be handled in the same
		510	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		511	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		512	methods called by the Perl core (== not by the user of the object) are
		513	usually in upper case letters and to avoid collisions with any C<to_json>
		514	function or method.
		515
		516	This setting does not yet influence C<decode> in any way, but in the
		517	future, global hooks might get installed that influence C<decode> and are
		518	enabled by this setting.
		519
		520	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		521	to do when a blessed object is found.
		522
		523	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		524
		525	When C<$coderef> is specified, it will be called from C<decode> each
		526	time it decodes a JSON object. The only argument is a reference to the
		527	newly-created hash. If the code references returns a single scalar (which
		528	need not be a reference), this value (i.e. a copy of that scalar to avoid
		529	aliasing) is inserted into the deserialised data structure. If it returns
		530	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		531	original deserialised hash will be inserted. This setting can slow down
		532	decoding considerably.
		533
		534	When C<$coderef> is omitted or undefined, any existing callback will
		535	be removed and C<decode> will not change the deserialised hash in any
		536	way.
		537
		538	Example, convert all JSON objects into the integer 5:
		539
		540	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		541	# returns [5]
		542	$js->decode ('[{}]')
		543	# throw an exception because allow_nonref is not enabled
		544	# so a lone 5 is not allowed.
		545	$js->decode ('{"a":1, "b":2}');
		546
		547	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		548
		549	Works remotely similar to C<filter_json_object>, but is only called for
		550	JSON objects having a single key named C<$key>.
		551
		552	This C<$coderef> is called before the one specified via
		553	C<filter_json_object>, if any. It gets passed the single value in the JSON
		554	object. If it returns a single value, it will be inserted into the data
		555	structure. If it returns nothing (not even C<undef> but the empty list),
		556	the callback from C<filter_json_object> will be called next, as if no
		557	single-key callback were specified.
		558
		559	If C<$coderef> is omitted or undefined, the corresponding callback will be
		560	disabled. There can only ever be one callback for a given key.
		561
		562	As this callback gets called less often then the C<filter_json_object>
		563	one, decoding speed will not usually suffer as much. Therefore, single-key
		564	objects make excellent targets to serialise Perl objects into, especially
		565	as single-key JSON objects are as close to the type-tagged value concept
		566	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		567	support this in any way, so you need to make sure your data never looks
		568	like a serialised Perl hash.
		569
		570	Typical names for the single object key are C<__class_whatever__>, or
		571	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		572	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		573	with real hashes.
		574
		575	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		576	into the corresponding C<< $WIDGET{<id>} >> object:
		577
		578	# return whatever is in $WIDGET{5}:
		579	JSON::XS
		580	->new
		581	->filter_json_single_key_object (__widget__ => sub {
		582	$WIDGET{ $_[0] }
		583	})
		584	->decode ('{"__widget__": 5')
		585
		586	# this can be used with a TO_JSON method in some "widget" class
		587	# for serialisation to json:
		588	sub WidgetBase::TO_JSON {
		589	my ($self) = @_;
		590
		591	unless ($self->{id}) {
		592	$self->{id} = ..get..some..id..;
		593	$WIDGET{$self->{id}} = $self;
		594	}
		595
		596	{ __widget__ => $self->{id} }
		597	}
		598
223	=item $json = $json->shrink ([$enable])	599	=item $json = $json->shrink ([$enable])
224		600
		601	=item $enabled = $json->get_shrink
		602
225	Perl usually over-allocates memory a bit when allocating space for	603	Perl usually over-allocates memory a bit when allocating space for
226	strings. This flag optionally resizes strings generated by either	604	strings. This flag optionally resizes strings generated by either
227	C<encode> or C<decode> to their minimum size possible. This can save	605	C<encode> or C<decode> to their minimum size possible. This can save
228	memory when your JSON strings are either very very long or you have many	606	memory when your JSON texts are either very very long or you have many
229	short strings.	607	short strings. It will also try to downgrade any strings to octet-form
		608	if possible: perl stores strings internally either in an encoding called
		609	UTF-X or in octet-form. The latter cannot store everything but uses less
		610	space in general (and some buggy Perl or C code might even rely on that
		611	internal representation being used).
230		612
		613	The actual definition of what shrink does might change in future versions,
		614	but it will always try to save space at the expense of time.
		615
231	If C<$enable> is true (or missing), the string returned by C<encode> will be shrunk-to-fit,	616	If C<$enable> is true (or missing), the string returned by C<encode> will
232	while all strings generated by C<decode> will also be shrunk-to-fit.	617	be shrunk-to-fit, while all strings generated by C<decode> will also be
		618	shrunk-to-fit.
233		619
234	If C<$enable> is false, then the normal perl allocation algorithms are used.	620	If C<$enable> is false, then the normal perl allocation algorithms are used.
235	If you work with your data, then this is likely to be faster.	621	If you work with your data, then this is likely to be faster.
236		622
237	In the future, this setting might control other things, such as converting	623	In the future, this setting might control other things, such as converting
238	strings that look like integers or floats into integers or floats	624	strings that look like integers or floats into integers or floats
239	internally (there is no difference on the Perl level), saving space.	625	internally (there is no difference on the Perl level), saving space.
240		626
		627	=item $json = $json->max_depth ([$maximum_nesting_depth])
		628
		629	=item $max_depth = $json->get_max_depth
		630
		631	Sets the maximum nesting level (default C<512>) accepted while encoding
		632	or decoding. If a higher nesting level is detected in JSON text or a Perl
		633	data structure, then the encoder and decoder will stop and croak at that
		634	point.
		635
		636	Nesting level is defined by number of hash- or arrayrefs that the encoder
		637	needs to traverse to reach a given point or the number of C<{> or C<[>
		638	characters without their matching closing parenthesis crossed to reach a
		639	given character in a string.
		640
		641	Setting the maximum depth to one disallows any nesting, so that ensures
		642	that the object is only a single hash/object or array.
		643
		644	If no argument is given, the highest possible setting will be used, which
		645	is rarely useful.
		646
		647	Note that nesting is implemented by recursion in C. The default value has
		648	been chosen to be as large as typical operating systems allow without
		649	crashing.
		650
		651	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		652
		653	=item $json = $json->max_size ([$maximum_string_size])
		654
		655	=item $max_size = $json->get_max_size
		656
		657	Set the maximum length a JSON text may have (in bytes) where decoding is
		658	being attempted. The default is C<0>, meaning no limit. When C<decode>
		659	is called on a string that is longer then this many bytes, it will not
		660	attempt to decode the string but throw an exception. This setting has no
		661	effect on C<encode> (yet).
		662
		663	If no argument is given, the limit check will be deactivated (same as when
		664	C<0> is specified).
		665
		666	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		667
241	=item $json_string = $json->encode ($perl_scalar)	668	=item $json_text = $json->encode ($perl_scalar)
242		669
243	Converts the given Perl data structure (a simple scalar or a reference	670	Converts the given Perl data structure (a simple scalar or a reference
244	to a hash or array) to its JSON representation. Simple scalars will be	671	to a hash or array) to its JSON representation. Simple scalars will be
245	converted into JSON string or number sequences, while references to arrays	672	converted into JSON string or number sequences, while references to arrays
246	become JSON arrays and references to hashes become JSON objects. Undefined	673	become JSON arrays and references to hashes become JSON objects. Undefined
247	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>	674	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
248	nor C<false> values will be generated.	675	nor C<false> values will be generated.
249		676
250	=item $perl_scalar = $json->decode ($json_string)	677	=item $perl_scalar = $json->decode ($json_text)
251		678
252	The opposite of C<encode>: expects a JSON string and tries to parse it,	679	The opposite of C<encode>: expects a JSON text and tries to parse it,
253	returning the resulting simple scalar or reference. Croaks on error.	680	returning the resulting simple scalar or reference. Croaks on error.
254		681
255	JSON numbers and strings become simple Perl scalars. JSON arrays become	682	JSON numbers and strings become simple Perl scalars. JSON arrays become
256	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes	683	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
257	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.	684	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
258		685
		686	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		687
		688	This works like the C<decode> method, but instead of raising an exception
		689	when there is trailing garbage after the first JSON object, it will
		690	silently stop parsing there and return the number of characters consumed
		691	so far.
		692
		693	This is useful if your JSON texts are not delimited by an outer protocol
		694	(which is not the brightest thing to do in the first place) and you need
		695	to know where the JSON text ends.
		696
		697	JSON::XS->new->decode_prefix ("[1] the tail")
		698	=> ([], 3)
		699
259	=back	700	=back
260		701
261	=head1 COMPARISON
262		702
263	As already mentioned, this module was created because none of the existing	703	=head1 INCREMENTAL PARSING
264	JSON modules could be made to work correctly. First I will describe the	704
265	problems (or pleasures) I encountered with various existing JSON modules,	705	In some cases, there is the need for incremental parsing of JSON
266	followed by some benchmark values. JSON::XS was designed not to suffer	706	texts. While this module always has to keep both JSON text and resulting
267	from any of these problems or limitations.	707	Perl data structure in memory at one time, it does allow you to parse a
		708	JSON stream incrementally. It does so by accumulating text until it has
		709	a full JSON object, which it then can decode. This process is similar to
		710	using C<decode_prefix> to see if a full JSON object is available, but
		711	is much more efficient (and can be implemented with a minimum of method
		712	calls).
		713
		714	JSON::XS will only attempt to parse the JSON text once it is sure it
		715	has enough text to get a decisive result, using a very simple but
		716	truly incremental parser. This means that it sometimes won't stop as
		717	early as the full parser, for example, it doesn't detect parenthese
		718	mismatches. The only thing it guarantees is that it starts decoding as
		719	soon as a syntactically valid JSON text has been seen. This means you need
		720	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		721	parsing in the presence if syntax errors.
		722
		723	The following methods implement this incremental parser.
268		724
269	=over 4	725	=over 4
270		726
271	=item JSON 1.07	727	=item [void, scalar or list context] = $json->incr_parse ([$string])
272		728
273	Slow (but very portable, as it is written in pure Perl).	729	This is the central parsing function. It can both append new text and
		730	extract objects from the stream accumulated so far (both of these
		731	functions are optional).
274		732
275	Undocumented/buggy Unicode handling (how JSON handles unicode values is	733	If C<$string> is given, then this string is appended to the already
276	undocumented. One can get far by feeding it unicode strings and doing	734	existing JSON fragment stored in the C<$json> object.
277	en-/decoding oneself, but unicode escapes are not working properly).
278		735
279	No roundtripping (strings get clobbered if they look like numbers, e.g.	736	After that, if the function is called in void context, it will simply
280	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will	737	return without doing anything further. This can be used to add more text
281	decode into the number 2.	738	in as many chunks as you want.
282		739
283	=item JSON::PC 0.01	740	If the method is called in scalar context, then it will try to extract
		741	exactly I<one> JSON object. If that is successful, it will return this
		742	object, otherwise it will return C<undef>. If there is a parse error,
		743	this method will croak just as C<decode> would do (one can then use
		744	C<incr_skip> to skip the errornous part). This is the most common way of
		745	using the method.
284		746
285	Very fast.	747	And finally, in list context, it will try to extract as many objects
		748	from the stream as it can find and return them, or the empty list
		749	otherwise. For this to work, there must be no separators between the JSON
		750	objects or arrays, instead they must be concatenated back-to-back. If
		751	an error occurs, an exception will be raised as in the scalar context
		752	case. Note that in this case, any previously-parsed JSON texts will be
		753	lost.
286		754
287	Undocumented/buggy Unicode handling.	755	=item $lvalue_string = $json->incr_text
288		756
289	No roundtripping.	757	This method returns the currently stored JSON fragment as an lvalue, that
		758	is, you can manipulate it. This I<only> works when a preceding call to
		759	C<incr_parse> in I<scalar context> successfully returned an object. Under
		760	all other circumstances you must not call this function (I mean it.
		761	although in simple tests it might actually work, it I<will> fail under
		762	real world conditions). As a special exception, you can also call this
		763	method before having parsed anything.
290		764
291	Has problems handling many Perl values (e.g. regex results and other magic	765	This function is useful in two cases: a) finding the trailing text after a
292	values will make it croak).	766	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		767	(such as commas).
293		768
294	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	769	=item $json->incr_skip
295	which is not a valid JSON string.
296		770
297	Unmaintained (maintainer unresponsive for many months, bugs are not	771	This will reset the state of the incremental parser and will remove the
298	getting fixed).	772	parsed text from the input buffer. This is useful after C<incr_parse>
		773	died, in which case the input buffer and incremental parser state is left
		774	unchanged, to skip the text parsed so far and to reset the parse state.
299		775
300	=item JSON::Syck 0.21	776	=item $json->incr_reset
301		777
302	Very buggy (often crashes).	778	This completely resets the incremental parser, that is, after this call,
		779	it will be as if the parser had never parsed anything.
303		780
304	Very inflexible (no human-readable format supported, format pretty much	781	This is useful if you want ot repeatedly parse JSON objects and want to
305	undocumented. I need at least a format for easy reading by humans and a	782	ignore any trailing data, which means you have to reset the parser after
306	single-line compact format for use in a protocol, and preferably a way to	783	each successful decode.
307	generate ASCII-only JSON strings).
308
309	Completely broken (and confusingly documented) Unicode handling (unicode
310	escapes are not working properly, you need to set ImplicitUnicode to
311	I<different> values on en- and decoding to get symmetric behaviour).
312
313	No roundtripping (simple cases work, but this depends on wether the scalar
314	value was used in a numeric context or not).
315
316	Dumping hashes may skip hash values depending on iterator state.
317
318	Unmaintained (maintainer unresponsive for many months, bugs are not
319	getting fixed).
320
321	Does not check input for validity (i.e. will accept non-JSON input and
322	return "something" instead of raising an exception. This is a security
323	issue: imagine two banks transfering money between each other using
324	JSON. One bank might parse a given non-JSON request and deduct money,
325	while the other might reject the transaction with a syntax error. While a
326	good protocol will at least recover, that is extra unnecessary work and
327	the transaction will still not succeed).
328
329	=item JSON::DWIW 0.04
330
331	Very fast. Very natural. Very nice.
332
333	Undocumented unicode handling (but the best of the pack. Unicode escapes
334	still don't get parsed properly).
335
336	Very inflexible.
337
338	No roundtripping.
339
340	Does not generate valid JSON (key strings are often unquoted, empty keys
341	result in nothing being output)
342
343	Does not check input for validity.
344		784
345	=back	785	=back
		786
		787	=head2 LIMITATIONS
		788
		789	All options that affect decoding are supported, except
		790	C<allow_nonref>. The reason for this is that it cannot be made to
		791	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		792	them back to back and still decode them perfectly. This does not hold true
		793	for JSON numbers, however.
		794
		795	For example, is the string C<1> a single JSON number, or is it simply the
		796	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		797	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		798	takes the conservative route and disallows this case.
		799
		800	=head2 EXAMPLES
		801
		802	Some examples will make all this clearer. First, a simple example that
		803	works similarly to C<decode_prefix>: We want to decode the JSON object at
		804	the start of a string and identify the portion after the JSON object:
		805
		806	my $text = "[1,2,3] hello";
		807
		808	my $json = new JSON::XS;
		809
		810	my $obj = $json->incr_parse ($text)
		811	or die "expected JSON object or array at beginning of string";
		812
		813	my $tail = $json->incr_text;
		814	# $tail now contains " hello"
		815
		816	Easy, isn't it?
		817
		818	Now for a more complicated example: Imagine a hypothetical protocol where
		819	you read some requests from a TCP stream, and each request is a JSON
		820	array, without any separation between them (in fact, it is often useful to
		821	use newlines as "separators", as these get interpreted as whitespace at
		822	the start of the JSON text, which makes it possible to test said protocol
		823	with C<telnet>...).
		824
		825	Here is how you'd do it (it is trivial to write this in an event-based
		826	manner):
		827
		828	my $json = new JSON::XS;
		829
		830	# read some data from the socket
		831	while (sysread $socket, my $buf, 4096) {
		832
		833	# split and decode as many requests as possible
		834	for my $request ($json->incr_parse ($buf)) {
		835	# act on the $request
		836	}
		837	}
		838
		839	Another complicated example: Assume you have a string with JSON objects
		840	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		841	[3]>). To parse them, we have to skip the commas between the JSON texts,
		842	and here is where the lvalue-ness of C<incr_text> comes in useful:
		843
		844	my $text = "[1],[2], [3]";
		845	my $json = new JSON::XS;
		846
		847	# void context, so no parsing done
		848	$json->incr_parse ($text);
		849
		850	# now extract as many objects as possible. note the
		851	# use of scalar context so incr_text can be called.
		852	while (my $obj = $json->incr_parse) {
		853	# do something with $obj
		854
		855	# now skip the optional comma
		856	$json->incr_text =~ s/^ \s* , //x;
		857	}
		858
		859	Now lets go for a very complex example: Assume that you have a gigantic
		860	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		861	but you cannot load it into memory fully (this has actually happened in
		862	the real world :).
		863
		864	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		865	can still help you: You implement a (very simple) array parser and let
		866	JSON decode the array elements, which are all full JSON objects on their
		867	own (this wouldn't work if the array elements could be JSON numbers, for
		868	example):
		869
		870	my $json = new JSON::XS;
		871
		872	# open the monster
		873	open my $fh, "<bigfile.json"
		874	or die "bigfile: $!";
		875
		876	# first parse the initial "["
		877	for (;;) {
		878	sysread $fh, my $buf, 65536
		879	or die "read error: $!";
		880	$json->incr_parse ($buf); # void context, so no parsing
		881
		882	# Exit the loop once we found and removed(!) the initial "[".
		883	# In essence, we are (ab-)using the $json object as a simple scalar
		884	# we append data to.
		885	last if $json->incr_text =~ s/^ \s* \[ //x;
		886	}
		887
		888	# now we have the skipped the initial "[", so continue
		889	# parsing all the elements.
		890	for (;;) {
		891	# in this loop we read data until we got a single JSON object
		892	for (;;) {
		893	if (my $obj = $json->incr_parse) {
		894	# do something with $obj
		895	last;
		896	}
		897
		898	# add more data
		899	sysread $fh, my $buf, 65536
		900	or die "read error: $!";
		901	$json->incr_parse ($buf); # void context, so no parsing
		902	}
		903
		904	# in this loop we read data until we either found and parsed the
		905	# separating "," between elements, or the final "]"
		906	for (;;) {
		907	# first skip whitespace
		908	$json->incr_text =~ s/^\s*//;
		909
		910	# if we find "]", we are done
		911	if ($json->incr_text =~ s/^\]//) {
		912	print "finished.\n";
		913	exit;
		914	}
		915
		916	# if we find ",", we can continue with the next element
		917	if ($json->incr_text =~ s/^,//) {
		918	last;
		919	}
		920
		921	# if we find anything else, we have a parse error!
		922	if (length $json->incr_text) {
		923	die "parse error near ", $json->incr_text;
		924	}
		925
		926	# else add more data
		927	sysread $fh, my $buf, 65536
		928	or die "read error: $!";
		929	$json->incr_parse ($buf); # void context, so no parsing
		930	}
		931
		932	This is a complex example, but most of the complexity comes from the fact
		933	that we are trying to be correct (bear with me if I am wrong, I never ran
		934	the above example :).
		935
		936
		937
		938	=head1 MAPPING
		939
		940	This section describes how JSON::XS maps Perl values to JSON values and
		941	vice versa. These mappings are designed to "do the right thing" in most
		942	circumstances automatically, preserving round-tripping characteristics
		943	(what you put in comes out as something equivalent).
		944
		945	For the more enlightened: note that in the following descriptions,
		946	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		947	refers to the abstract Perl language itself.
		948
		949
		950	=head2 JSON -> PERL
		951
		952	=over 4
		953
		954	=item object
		955
		956	A JSON object becomes a reference to a hash in Perl. No ordering of object
		957	keys is preserved (JSON does not preserve object key ordering itself).
		958
		959	=item array
		960
		961	A JSON array becomes a reference to an array in Perl.
		962
		963	=item string
		964
		965	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		966	are represented by the same codepoints in the Perl string, so no manual
		967	decoding is necessary.
		968
		969	=item number
		970
		971	A JSON number becomes either an integer, numeric (floating point) or
		972	string scalar in perl, depending on its range and any fractional parts. On
		973	the Perl level, there is no difference between those as Perl handles all
		974	the conversion details, but an integer may take slightly less memory and
		975	might represent more values exactly than floating point numbers.
		976
		977	If the number consists of digits only, JSON::XS will try to represent
		978	it as an integer value. If that fails, it will try to represent it as
		979	a numeric (floating point) value if that is possible without loss of
		980	precision. Otherwise it will preserve the number as a string value (in
		981	which case you lose roundtripping ability, as the JSON number will be
		982	re-encoded toa JSON string).
		983
		984	Numbers containing a fractional or exponential part will always be
		985	represented as numeric (floating point) values, possibly at a loss of
		986	precision (in which case you might lose perfect roundtripping ability, but
		987	the JSON number will still be re-encoded as a JSON number).
		988
		989	=item true, false
		990
		991	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		992	respectively. They are overloaded to act almost exactly like the numbers
		993	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		994	the C<JSON::XS::is_bool> function.
		995
		996	=item null
		997
		998	A JSON null atom becomes C<undef> in Perl.
		999
		1000	=back
		1001
		1002
		1003	=head2 PERL -> JSON
		1004
		1005	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		1006	truly typeless language, so we can only guess which JSON type is meant by
		1007	a Perl value.
		1008
		1009	=over 4
		1010
		1011	=item hash references
		1012
		1013	Perl hash references become JSON objects. As there is no inherent ordering
		1014	in hash keys (or JSON objects), they will usually be encoded in a
		1015	pseudo-random order that can change between runs of the same program but
		1016	stays generally the same within a single run of a program. JSON::XS can
		1017	optionally sort the hash keys (determined by the I<canonical> flag), so
		1018	the same datastructure will serialise to the same JSON text (given same
		1019	settings and version of JSON::XS), but this incurs a runtime overhead
		1020	and is only rarely useful, e.g. when you want to compare some JSON text
		1021	against another for equality.
		1022
		1023	=item array references
		1024
		1025	Perl array references become JSON arrays.
		1026
		1027	=item other references
		1028
		1029	Other unblessed references are generally not allowed and will cause an
		1030	exception to be thrown, except for references to the integers C<0> and
		1031	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		1032	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		1033
		1034	encode_json [\0, JSON::XS::true] # yields [false,true]
		1035
		1036	=item JSON::XS::true, JSON::XS::false
		1037
		1038	These special values become JSON true and JSON false values,
		1039	respectively. You can also use C<\1> and C<\0> directly if you want.
		1040
		1041	=item blessed objects
		1042
		1043	Blessed objects are not directly representable in JSON. See the
		1044	C<allow_blessed> and C<convert_blessed> methods on various options on
		1045	how to deal with this: basically, you can choose between throwing an
		1046	exception, encoding the reference as if it weren't blessed, or provide
		1047	your own serialiser method.
		1048
		1049	=item simple scalars
		1050
		1051	Simple Perl scalars (any scalar that is not a reference) are the most
		1052	difficult objects to encode: JSON::XS will encode undefined scalars as
		1053	JSON C<null> values, scalars that have last been used in a string context
		1054	before encoding as JSON strings, and anything else as number value:
		1055
		1056	# dump as number
		1057	encode_json [2] # yields [2]
		1058	encode_json [-3.0e17] # yields [-3e+17]
		1059	my $value = 5; encode_json [$value] # yields [5]
		1060
		1061	# used as string, so dump as string
		1062	print $value;
		1063	encode_json [$value] # yields ["5"]
		1064
		1065	# undef becomes null
		1066	encode_json [undef] # yields [null]
		1067
		1068	You can force the type to be a JSON string by stringifying it:
		1069
		1070	my $x = 3.1; # some variable containing a number
		1071	"$x"; # stringified
		1072	$x .= ""; # another, more awkward way to stringify
		1073	print $x; # perl does it for you, too, quite often
		1074
		1075	You can force the type to be a JSON number by numifying it:
		1076
		1077	my $x = "3"; # some variable containing a string
		1078	$x += 0; # numify it, ensuring it will be dumped as a number
		1079	$x *= 1; # same thing, the choice is yours.
		1080
		1081	You can not currently force the type in other, less obscure, ways. Tell me
		1082	if you need this capability (but don't forget to explain why it's needed
		1083	:).
		1084
		1085	=back
		1086
		1087
		1088	=head1 ENCODING/CODESET FLAG NOTES
		1089
		1090	The interested reader might have seen a number of flags that signify
		1091	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1092	some confusion on what these do, so here is a short comparison:
		1093
		1094	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1095	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1096	control whether C<encode> escapes character values outside their respective
		1097	codeset range. Neither of these flags conflict with each other, although
		1098	some combinations make less sense than others.
		1099
		1100	Care has been taken to make all flags symmetrical with respect to
		1101	C<encode> and C<decode>, that is, texts encoded with any combination of
		1102	these flag values will be correctly decoded when the same flags are used
		1103	- in general, if you use different flag settings while encoding vs. when
		1104	decoding you likely have a bug somewhere.
		1105
		1106	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1107	simply an abstract set of character-codepoint pairs, while an encoding
		1108	takes those codepoint numbers and I<encodes> them, in our case into
		1109	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1110	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1111	the same time, which can be confusing.
		1112
		1113	=over 4
		1114
		1115	=item C<utf8> flag disabled
		1116
		1117	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1118	and expect Unicode strings, that is, characters with high ordinal Unicode
		1119	values (> 255) will be encoded as such characters, and likewise such
		1120	characters are decoded as-is, no canges to them will be done, except
		1121	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1122	respectively (to Perl, these are the same thing in strings unless you do
		1123	funny/weird/dumb stuff).
		1124
		1125	This is useful when you want to do the encoding yourself (e.g. when you
		1126	want to have UTF-16 encoded JSON texts) or when some other layer does
		1127	the encoding for you (for example, when printing to a terminal using a
		1128	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1129	to UTF-8 encode your data first and have Perl encode it another time).
		1130
		1131	=item C<utf8> flag enabled
		1132
		1133	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1134	characters using the corresponding UTF-8 multi-byte sequence, and will
		1135	expect your input strings to be encoded as UTF-8, that is, no "character"
		1136	of the input string must have any value > 255, as UTF-8 does not allow
		1137	that.
		1138
		1139	The C<utf8> flag therefore switches between two modes: disabled means you
		1140	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1141	octet/binary string in Perl.
		1142
		1143	=item C<latin1> or C<ascii> flags enabled
		1144
		1145	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1146	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1147	characters as specified by the C<utf8> flag.
		1148
		1149	If C<utf8> is disabled, then the result is also correctly encoded in those
		1150	character sets (as both are proper subsets of Unicode, meaning that a
		1151	Unicode string with all character values < 256 is the same thing as a
		1152	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1153	the same thing as an ASCII string in Perl).
		1154
		1155	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1156	regardless of these flags, just some more characters will be escaped using
		1157	C<\uXXXX> then before.
		1158
		1159	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1160	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1161	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1162	a subset of Unicode), while ASCII is.
		1163
		1164	Surprisingly, C<decode> will ignore these flags and so treat all input
		1165	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1166	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1167	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1168
		1169	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1170	they only govern when the JSON output engine escapes a character or not.
		1171
		1172	The main use for C<latin1> is to relatively efficiently store binary data
		1173	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1174
		1175	The main use for C<ascii> is to force the output to not contain characters
		1176	with values > 127, which means you can interpret the resulting string
		1177	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1178	8-bit-encoding, and still get the same data structure back. This is useful
		1179	when your channel for JSON transfer is not 8-bit clean or the encoding
		1180	might be mangled in between (e.g. in mail), and works because ASCII is a
		1181	proper subset of most 8-bit and multibyte encodings in use in the world.
		1182
		1183	=back
		1184
		1185
		1186	=head2 JSON and YAML
		1187
		1188	You often hear that JSON is a subset of YAML. This is, however, a mass
		1189	hysteria(*) and very far from the truth (as of the time of this writing),
		1190	so let me state it clearly: I<in general, there is no way to configure
		1191	JSON::XS to output a data structure as valid YAML> that works in all
		1192	cases.
		1193
		1194	If you really must use JSON::XS to generate YAML, you should use this
		1195	algorithm (subject to change in future versions):
		1196
		1197	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1198	my $yaml = $to_yaml->encode ($ref) . "\n";
		1199
		1200	This will I<usually> generate JSON texts that also parse as valid
		1201	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1202	lengths that JSON doesn't have and also has different and incompatible
		1203	unicode handling, so you should make sure that your hash keys are
		1204	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1205	you do not have characters with codepoint values outside the Unicode BMP
		1206	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1207	strings (which JSON::XS does not I<currently> generate, but other JSON
		1208	generators might).
		1209
		1210	There might be other incompatibilities that I am not aware of (or the YAML
		1211	specification has been changed yet again - it does so quite often). In
		1212	general you should not try to generate YAML with a JSON generator or vice
		1213	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1214	high that you will run into severe interoperability problems when you
		1215	least expect it.
		1216
		1217	=over 4
		1218
		1219	=item (*)
		1220
		1221	I have been pressured multiple times by Brian Ingerson (one of the
		1222	authors of the YAML specification) to remove this paragraph, despite him
		1223	acknowledging that the actual incompatibilities exist. As I was personally
		1224	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1225	educate people about these issues, so others do not run into the same
		1226	problem again and again. After this, Brian called me a (quote)I<complete
		1227	and worthless idiot>(unquote).
		1228
		1229	In my opinion, instead of pressuring and insulting people who actually
		1230	clarify issues with YAML and the wrong statements of some of its
		1231	proponents, I would kindly suggest reading the JSON spec (which is not
		1232	that difficult or long) and finally make YAML compatible to it, and
		1233	educating users about the changes, instead of spreading lies about the
		1234	real compatibility for many I<years> and trying to silence people who
		1235	point out that it isn't true.
		1236
		1237	=back
		1238
346		1239
347	=head2 SPEED	1240	=head2 SPEED
348		1241
349	It seems that JSON::XS is surprisingly fast, as shown in the following	1242	It seems that JSON::XS is surprisingly fast, as shown in the following
350	tables. They have been generated with the help of the C<eg/bench> program	1243	tables. They have been generated with the help of the C<eg/bench> program
351	in the JSON::XS distribution, to make it easy to compare on your own	1244	in the JSON::XS distribution, to make it easy to compare on your own
352	system.	1245	system.
353		1246
354	First is a comparison between various modules using a very simple JSON	1247	First comes a comparison between various modules using
		1248	a very short single-line JSON string (also available at
		1249	L<http://dist.schmorp.de/misc/json/short.json>).
		1250
		1251	{"method": "handleMessage", "params": ["user1",
		1252	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1253	true, false]}
		1254
355	string, showing the number of encodes/decodes per second (JSON::XS is	1255	It shows the number of encodes/decodes per second (JSON::XS uses
356	the functional interface, while JSON::XS/2 is the OO interface with	1256	the functional interface, while JSON::XS/2 uses the OO interface
357	pretty-printing and hashkey sorting enabled).	1257	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1258	shrink). Higher is better:
358		1259
359	module | encode | decode |	1260	module | encode | decode |
360	-----------|------------|------------|	1261	-----------|------------|------------|
361	JSON | 14006 | 6820 |	1262	JSON 1.x | 4990.842 | 4088.813 |
362	JSON::DWIW | 200937 | 120386 |	1263	JSON::DWIW | 51653.990 | 71575.154 |
363	JSON::PC | 85065 | 129366 |	1264	JSON::PC | 65948.176 | 74631.744 |
364	JSON::Syck | 59898 | 44232 |	1265	JSON::PP | 8931.652 | 3817.168 |
365	JSON::XS | 1171478 | 342435 |	1266	JSON::Syck | 24877.248 | 27776.848 |
366	JSON::XS/2 | 730760 | 328714 |	1267	JSON::XS | 388361.481 | 227951.304 |
		1268	JSON::XS/2 | 227951.304 | 218453.333 |
		1269	JSON::XS/3 | 338250.323 | 218453.333 |
		1270	Storable | 16500.016 | 135300.129 |
367	-----------+------------+------------+	1271	-----------+------------+------------+
368		1272
369	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	1273	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1274	about three times faster on decoding, and over forty times faster
370	times faster than JSON, even with pretty-printing and key sorting.	1275	than JSON, even with pretty-printing and key sorting. It also compares
		1276	favourably to Storable for small amounts of data.
371		1277
372	Using a longer test string (roughly 8KB, generated from Yahoo! Locals	1278	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
373	search API (http://nanoref.com/yahooapis/mgPdGg):	1279	search API (L<http://dist.schmorp.de/misc/json/long.json>).
374		1280
375	module | encode | decode |	1281	module | encode | decode |
376	-----------|------------|------------|	1282	-----------|------------|------------|
377	JSON | 673 | 38 |	1283	JSON 1.x | 55.260 | 34.971 |
378	JSON::DWIW | 5271 | 770 |	1284	JSON::DWIW | 825.228 | 1082.513 |
379	JSON::PC | 9901 | 2491 |	1285	JSON::PC | 3571.444 | 2394.829 |
380	JSON::Syck | 2360 | 786 |	1286	JSON::PP | 210.987 | 32.574 |
381	JSON::XS | 37398 | 3202 |	1287	JSON::Syck | 552.551 | 787.544 |
382	JSON::XS/2 | 13765 | 3153 |	1288	JSON::XS | 5780.463 | 4854.519 |
		1289	JSON::XS/2 | 3869.998 | 4798.975 |
		1290	JSON::XS/3 | 5862.880 | 4798.975 |
		1291	Storable | 4445.002 | 5235.027 |
383	-----------+------------+------------+	1292	-----------+------------+------------+
384		1293
385	Again, JSON::XS leads by far in the encoding case, while still beating	1294	Again, JSON::XS leads by far (except for Storable which non-surprisingly
386	every other module in the decoding case.	1295	decodes faster).
387		1296
388	Last example is an almost 8MB large hash with many large binary values	1297	On large strings containing lots of high Unicode characters, some modules
389	(PNG files), resulting in a lot of escaping:	1298	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1299	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1300	to decode or encode properly, so it was impossible to prepare a fair
		1301	comparison table for that case.
		1302
		1303
		1304	=head1 SECURITY CONSIDERATIONS
		1305
		1306	When you are using JSON in a protocol, talking to untrusted potentially
		1307	hostile creatures requires relatively few measures.
		1308
		1309	First of all, your JSON decoder should be secure, that is, should not have
		1310	any buffer overflows. Obviously, this module should ensure that and I am
		1311	trying hard on making that true, but you never know.
		1312
		1313	Second, you need to avoid resource-starving attacks. That means you should
		1314	limit the size of JSON texts you accept, or make sure then when your
		1315	resources run out, that's just fine (e.g. by using a separate process that
		1316	can crash safely). The size of a JSON text in octets or characters is
		1317	usually a good indication of the size of the resources required to decode
		1318	it into a Perl structure. While JSON::XS can check the size of the JSON
		1319	text, it might be too late when you already have it in memory, so you
		1320	might want to check the size before you accept the string.
		1321
		1322	Third, JSON::XS recurses using the C stack when decoding objects and
		1323	arrays. The C stack is a limited resource: for instance, on my amd64
		1324	machine with 8MB of stack size I can decode around 180k nested arrays but
		1325	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1326	to free the temporary). If that is exceeded, the program crashes. To be
		1327	conservative, the default nesting limit is set to 512. If your process
		1328	has a smaller stack, you should adjust this setting accordingly with the
		1329	C<max_depth> method.
		1330
		1331	Something else could bomb you, too, that I forgot to think of. In that
		1332	case, you get to keep the pieces. I am always open for hints, though...
		1333
		1334	Also keep in mind that JSON::XS might leak contents of your Perl data
		1335	structures in its error messages, so when you serialise sensitive
		1336	information you might want to make sure that exceptions thrown by JSON::XS
		1337	will not end up in front of untrusted eyes.
		1338
		1339	If you are using JSON::XS to return packets to consumption
		1340	by JavaScript scripts in a browser you should have a look at
		1341	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1342	you are vulnerable to some common attack vectors (which really are browser
		1343	design bugs, but it is still you who will have to deal with it, as major
		1344	browser developers care only for features, not about getting security
		1345	right).
		1346
		1347
		1348	=head1 THREADS
		1349
		1350	This module is I<not> guaranteed to be thread safe and there are no
		1351	plans to change this until Perl gets thread support (as opposed to the
		1352	horribly slow so-called "threads" which are simply slow and bloated
		1353	process simulations - use fork, it's I<much> faster, cheaper, better).
		1354
		1355	(It might actually work, but you have been warned).
		1356
390		1357
391	=head1 BUGS	1358	=head1 BUGS
392		1359
393	While the goal of this module is to be correct, that unfortunately does	1360	While the goal of this module is to be correct, that unfortunately does
394	not mean its bug-free, only that I think its design is bug-free. It is	1361	not mean it's bug-free, only that I think its design is bug-free. If you
395	still very young and not well-tested. If you keep reporting bugs they will	1362	keep reporting bugs they will be fixed swiftly, though.
396	be fixed swiftly, though.	1363
		1364	Please refrain from using rt.cpan.org or any other bug reporting
		1365	service. I put the contact address into my modules for a reason.
397		1366
398	=cut	1367	=cut
399		1368
		1369	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
		1370	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
		1371
		1372	sub true() { $true }
		1373	sub false() { $false }
		1374
		1375	sub is_bool($) {
		1376	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
		1377	# or UNIVERSAL::isa $_[0], "JSON::Literal"
		1378	}
		1379
		1380	XSLoader::load "JSON::XS", $VERSION;
		1381
		1382	package JSON::XS::Boolean;
		1383
		1384	use overload
		1385	"0+" => sub { ${$_[0]} },
		1386	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1387	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1388	fallback => 1;
		1389
400	1;	1390	1;
		1391
		1392	=head1 SEE ALSO
		1393
		1394	The F<json_xs> command line utility for quick experiments.
401		1395
402	=head1 AUTHOR	1396	=head1 AUTHOR
403		1397
404	Marc Lehmann <schmorp@schmorp.de>	1398	Marc Lehmann <schmorp@schmorp.de>
405	http://home.schmorp.de/	1399	http://home.schmorp.de/

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